The present invention relates to a process for preparing ruthenium(0)-olefin complexes of the (arene)(diene)Ru(0) type. These complexes are organometallic ruthenium compounds in which the central ruthenium atom has the +−0 oxidation state and is bound in the manner of a sandwich between two olefinic ligands. In these complexes, the arene group provides three double bonds and the diene group two double bonds, each in π-bonded coordination, to the central Ru(0) atom.
In the process according to the invention, an Ru(II) starting compound of the formula Ru(II)Xp(Y)q is reacted in the presence of a base with a suitable cyclohexadiene derivative, which acts as a reducing agent, is oxidized to the arene ligand and is coordinated in this form to the central atom which has been reduced to Ru(0). The corresponding Ru(0)-olefin compounds are obtained in high purity and good yield.
Ruthenium(0) complexes are gaining increasing significance as starting materials for preparation of homogeneous catalysts. The compounds also find use as precursors for obtaining functional coatings with the aid of thin-layer processes, for example MO-CVD (metal-organic chemical vapour deposition), PVD (physical vapour deposition) or ALD (atomic layer deposition). Ru(0) complexes can also have therapeutic effects and find uses in medicine, for example as cytostatics.
The literature discloses various processes for preparing ruthenium(0)-olefin complexes. Most of these compounds additionally contain CO ligands. The frequently used complexes of this class, for example (1,3-cyclohexadiene)Ru(CO)3 or (1,5-cyclooctadiene)Ru(CO)3, are prepared by reacting trisruthenium dodecacarbonyl (Ru3(CO)12) with the corresponding diene (on this subject, cf., for example U.S. Pat. No. 7,238,822).
WO 2008/078296A1 discloses Ru(0) complexes which contain an arene group and a diene group. They are used to prepare Ru or RuO2 films by means of CVD or ALD. The Ru(0) complexes are prepared in a two-stage process, in which a cyclohexadiene ligand is first reacted with Ru(III) chloride in an alcohol. This forms the dimeric complex [(arene)Ru(II)Cl2]2. This dimeric intermediate is converted by addition of a further diene ligand to the compound of the (arene)(diene)Ru(0) type. The disadvantage here is that the process is performed in two stages and, in the second stage, a diene excess is used, which leads to contaminated products. Moreover, the yields are reduced by the multistage process.
US 2009/0238970 A1 describes Ru(0) complexes of the (arene)(norbornadiene)Ru(0) type, which contain norbornadiene as the diene. The Ru(0) complexes are likewise prepared in a two-stage process via the dimeric complex [(arene)Ru(II)Cl2]2. The dimeric intermediate is converted by addition of norbornadiene in excess and of a base to a compound of the (arene)(norbornadiene)Ru(0) type. Here too, the process has two stages and is afflicted with the disadvantages already mentioned.
EP 1,604,964B1 describes a process for preparing Ru(0) complexes of the (arene)(diene)Ru(0) type, in which the dimeric starting compound [(arene)Ru(II)Cl2]2 is reacted with a corresponding diene ligand under reducing conditions. The crude product is purified and isolated by hot extraction with a saturated hydrocarbon solvent. The process again has two stages and generally has to be carried out under inert and anhydrous conditions.
A. Salzer et al. (Organometallics 2000, 19, p. 5471-5476) describe a process for preparing (η6-benzene)(η4-1,3-cyclohexadiene)ruthenium(0), in which the dichloro(2,7-dimethylocta-2,6-diene-1,8-diyl)ruthenium(IV) starting compound is reacted with cyclohexadiene in excess. The process has the disadvantage that the Ru(IV) starting compound has to be prepared in a complex process. In the event that the reduction does not proceed quantitatively, residues of Ru(III) or Ru(IV) and polymeric components may remain. As a result, the process is costly overall and barely suitable for industrial use.
P. Pertici and G. Vitulli (J.C.S. Dalton Trans., 1980, p. 1961-1964) describe a process for preparing cyclic ruthenium-olefin complexes, especially of (η6-benzene)(η4-1,3-cyclohexadiene)ruthenium(0) and (η6-cyclooctatriene)(η4-1,5-cyclooctadiene)ruthenium(0), in which the ruthenium(III) trichloride hydrate starting compound is reacted with a large (generally 30- to 50-fold) excess of corresponding diene ligand in the presence of excess zinc dust as a reducing agent. This results in a disproportionation reaction of the diene used to form the corresponding triene and the monoene. As a result of this, and owing to the high olefin excess, the product is additionally contaminated by polymeric and oligomeric substances. In addition, residues of zinc may remain and contaminate the product.
It was therefore an object of the present invention to provide a process for preparing ruthenium(0)-olefin complexes which provides products in high purity and high yield and is suitable for economic industrial application. The process should also have one stage and be based on starting compounds preparable in a simple manner.